The present invention relates to a wind-up device for vehicle safety belts, particularly for use in automobiles.
In order to avoid the so-called film reel effect of conventional belt winding devices, designs are known which include a belt brake device that engages when the winding drum is blocked. This braking device generally includes a braking roller which is adjustably held against the power of a spring and which is surrounded at least in part by the belt before the belt is wound on the drum. If the winding drum is blocked, this roller is displaced into a braking position by a tension force developed in the belt, creating a friction force which stops the belt. This prevents the turns of the belt, which may be wound relatively loosely on the drum, from being pulled tightly together by the belt tension, for example when there is an automobile accident. If the turns could be pulled together then, in spite of the blocked winding drum, there would result a relatively great extension of the belt which, without absorbing any significant amount of energy, would undesirably increase the forward displacement of the passenger in the vehicle, this being essentially the film reel effect.
In a prior art belt braking device, the brake roller actuates a brake element which clamps the belt into a stationary member. In another known device, the belt is braked in that the brake roller is brought into contact with a stationary member and removal of the belt is prevented merely by friction between the belt, which is wound about part of the roller, and the circumference of the brake roller which has been constructed to have a high coefficient of friction.
Both of the above-described devices are relatively complicated, particularly when reliable stopping of the belt is to be attained in order to prevent lengthening of the belt as this would require a considerable enlargement of the space provided for the wind-up device as well as a considerable increase in the number of required components.